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Feature Toggles

SAP BTP Feature Toggle Library

SAP BTP feature toggle library enables Node.js applications using the SAP Cloud Application Programming Model to maintain live-updatable feature toggles via Redis.

Getting Started (CAP Feature Toggles)

  • Set up project with @sap/cds.

  • Install library:

    npm install --save @cap-js-community/feature-toggle-library
  • For CAP Feature Toggles everything is configured automatically.
  • The library acts as a CDS-Plugin and registers a FeatureService, which can be used to check and update toggles.
  • For details see Example CAP Server.

Getting Started (Custom Configuration)

  • Same as previous section.

  • Write toggles.yaml configuration file:

    # info: check api priority; 0 means access is disabled
/check/priority:
  type: number
  fallbackValue: 0
  validations:
    - scopes: [user, tenant]
    - regex: '^\d+$'

  • Add configuration path to package.json:

    {
  "cds": {
    "featureToggles": {
      "configFile": "./toggles.yaml"
    }
  }
}

  • Write usage code in handlers:

    const toggles = require("@cap-js-community/feature-toggle-library");

const priorityHandler = async (context) => {
  const user = context.user.id;
  const tenant = context.tenant;
  const value = toggles.getFeatureValue("/check/priority", { user, tenant });
  if (value <= 0) {
    return context.reject("blocked");
  } else if (value < 10) {
    return context.reply("welcome");
  } else {
    return context.reply("very welcome");
  }
};

Features

  • Maintain feature toggle states consistently across multiple app instances.
  • Feature toggle changes are published from Redis to subscribed app instances with publish/subscribe pattern PUB/SUB.
  • Horizontal app scaling is supported and new app instances will start with the correct state, or fallback values, if they cannot connect to Redis.
  • Feature toggle values can be changed specifically for accessors with certain scopes, e.g., for specific tenants, users,…
  • Users can register change handler callbacks for specific toggles.
  • Users can register custom input validation callbacks for specific toggles.
  • Works as a CDS-Plugin and provides a REST service to read and manipulate toggles.

Peers

Further Topics